Converting binary file to Base64 string.

Question

Hi,

I need to convert uploaded binary files to base64 string format on the fly. I'm using ASP, Vbscript. Using Midori's component for base64 conversion. For small size files (<20K) the performance is okay. But when it exceeds 75 or 100K, its totally lost. Is there any efficient way to convert big binary files (2MB) to base64 string format?

Thanks in advance, Kenney

Answer 1

you should use the .NET methods Convert.ToBase64String and Convert.FromBase64String.

Use the Convert.FromBase64String( ) method. This will give you the binary data back (as a byte array).

To convert binary data to a Base64 string see conversion functions from binary data to a string in vbscript

from http://www.motobit.com/tips/detpg_Base64Encode/

Function Base64EncodeBinary(inData)
  Base64EncodeBinary = Base64Encode(BinaryToString(inData))
End Function

Function Base64Encode(inData)
  'rfc1521
  '2001 Antonin Foller, Motobit Software, http://Motobit.cz
  Const Base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
  Dim cOut, sOut, I

  'For each group of 3 bytes
  For I = 1 To Len(inData) Step 3
    Dim nGroup, pOut, sGroup

    'Create one long from this 3 bytes.
    nGroup = &H10000 * Asc(Mid(inData, I, 1)) + _
      &H100 * MyASC(Mid(inData, I + 1, 1)) + MyASC(Mid(inData, I + 2, 1))

    'Oct splits the long To 8 groups with 3 bits
    nGroup = Oct(nGroup)

    'Add leading zeros
    nGroup = String(8 - Len(nGroup), "0") & nGroup

    'Convert To base64
    pOut = Mid(Base64, CLng("&o" & Mid(nGroup, 1, 2)) + 1, 1) + _
      Mid(Base64, CLng("&o" & Mid(nGroup, 3, 2)) + 1, 1) + _
      Mid(Base64, CLng("&o" & Mid(nGroup, 5, 2)) + 1, 1) + _
      Mid(Base64, CLng("&o" & Mid(nGroup, 7, 2)) + 1, 1)

    'Add the part To OutPut string
    sOut = sOut + pOut

    'Add a new line For Each 76 chars In dest (76*3/4 = 57)
    'If (I + 2) Mod 57 = 0 Then sOut = sOut + vbCrLf
  Next
  Select Case Len(inData) Mod 3
    Case 1: '8 bit final
      sOut = Left(sOut, Len(sOut) - 2) + "=="
    Case 2: '16 bit final
      sOut = Left(sOut, Len(sOut) - 1) + "="
  End Select
  Base64Encode = sOut
End Function

Function MyASC(OneChar)
  If OneChar = "" Then MyASC = 0 Else MyASC = Asc(OneChar)
End Function

Answer 2

Use MSXML to do the encoding for you. Here is function encapsulating the procedure:-

 Function ToBase64(rabyt)

     Dim xml: Set xml = CreateObject("MSXML2.DOMDocument.3.0")
     xml.LoadXml "<root />"
     xml.documentElement.dataType = "bin.base64"
     xml.documentElement.nodeTypedValue = rabyt

     ToBase64 = xml.documentElement.Text

 End Function

Note this will include linebreaks in the base64 encoding but most base64 decoders are tolerant of linebreaks. If not you could simpy use Replace(base64, vbLF, "") to remove them, this will still be quicker than a pure VBScript solution.

Edit Example usage:-

Dim sBase64: sBase64 = ToBase64(Request.BinaryRead(Request.TotalBytes))

Answer 3

I use next code for c#:

    public static string ImageToBase64(Image image, ImageFormat format)
    {
        using (MemoryStream ms = new MemoryStream())
        {
            // Convert Image to byte[]
            image.Save(ms, format);
            byte[] imageBytes = ms.ToArray();

            // Convert byte[] to Base64 String
            string base64String = Convert.ToBase64String(imageBytes);
            return base64String;
        }
    }

    public static Image Base64ToImage(string base64String)
    {
        // Convert Base64 String to byte[]
        byte[] imageBytes = Convert.FromBase64String(base64String);
        MemoryStream ms = new MemoryStream(imageBytes, 0,
          imageBytes.Length);

        // Convert byte[] to Image
        ms.Write(imageBytes, 0, imageBytes.Length);
        Image image = Image.FromStream(ms, true);
        return image;
    }

for vbscript see http://www.freevbcode.com/ShowCode.asp?ID=5248 maybe help you.

Answer 4

There is a good discussion of this in base64-encode-string-in-vbscript.

In addition, I have found this site useful for trying to eek speed out of vb code. There are several variants of base 64 there for vb6 that are quite fast.

Answer 5

I have solved this issue by implementing a .net component for converting to base64 string. The hard part is the binary data sent to the .net COM from ASP is received as a string. Convert.ToBase64() accepts only byte[]. So I tried converting string to byte[].

But the encoding available in .net (Unicode, ASCII, UTF) doesn't works fine. There are data loss, while these encodings are used. Finally I get it done by using StringReader object. Read char by char(16 bit) and converted them to (8 bit) byte[] array.

And the performance is best.

Regards, Siva.